Washington's Birthday has a history as old as our country. It was celebrated publicly for the first time in the late 18th century, while George Washington was still president.
George Washington was born on either Feb. 11, 1731 or Feb. 22, 1732 depending on which calendar you consult.
At the time, England and its colonies were following the Julian calendar , instituted in 46 B.C. by the eponymous Julius Caesar. By that calendar, Washington was born on Feb. 11, 1731. But in 1752, England switched to the Gregorian calendar, which is still in use today, and that threw everything off.
Washington's Birthday became official in 1885, when President Chester Arthur signed a bill making it a federal holiday. Meanwhile, there was President Lincoln's birthday on Feb. 12, which never became a federal holiday but was celebrated as a legal holiday in many states outside the old Confederacy.
In 1968, Congress passed the Monday Holidays Act, which moved the official observance of Washington's birthday from Feb. 22 to the third Monday in February. Some reformers had wanted to change the name of the holiday as well, to Presidents' Day, in honor of both Lincoln and Washington, but that proposal was rejected by Congress, and the holiday remained officially Washington's Birthday.
Nevertheless, there was a popular misconception that the day had been officially renamed, a misconception only reinforced by the fact that the third Monday in February can only occur between Feb. 15 and Feb. 21. This means that the holiday is always after Lincoln's birthday and before Washington's birthday, without ever coinciding with either. Furthermore, some states which had previously celebrated Lincoln's Birthday dropped the observance after the federal holiday reforms, supporting the notion that the two presidential birthdays had been combined.
While the name change has never been authorized by Congress, it has gained a strong hold on the public consciousness, and is generally used on calendars, in advertising, and even by many government agencies. There have been attempts to introduce legislation requiring federal agencies to call the day Washington's Birthday, but these have never gotten very far. No matter what's in the law books, the popular usage is now well established.